The present invention applies to engine control systems and particularly to throttle control systems.
Many vehicle throttle control systems now use electrical circuitry to deliver an electrical signal from the accelerator or throttle control device, e.g., an accelerator pedal or hand control lever, to an electronic control system, e.g., fuel delivery system. For example, a voltage signal provided to the electronic fuel control system corresponds to accelerator pedal or hand control position. When an "in-range" voltage level arrives at the electronic fuel control system, the electronic fuel control system responds by injecting a corresponding volume of fuel into the engine fuel system.
In some applications, an accelerator control device failure can result in an invalid in-range throttle condition, i.e., an unintended in-range voltage level. Under such condition, even though the accelerator control device is at, for example, an idle position, the electronic fuel control system receives an erroneous throttle control signal and undesirably injects fuel into the engine fuel system. Loss of engine throttle control, and possibly unintended vehicle acceleration, can result.
To avoid such an error condition, a separate idle validation switch has been added to the accelerator control device as backup protection against such a failure. For example, U.S. Pat. No. 4,958,607 issued Sep. 25, 1990 to Lundberg and entitled Foot Pedal Arrangement For Electronic Throttle Control Of Truck Engines shows a throttle control arrangement in FIG. 1 including separately mounted a micro-switch responsive to a given position of the pedal for delivery of a idle validation signal to a computer controlling engine throttle functions. Typically, this switch provides a function wherein one side of the switch delivers a logic signal corresponding to valid idle operation and the other side validates throttle active operation. The switch slidably mounts to the accelerator control device in such a way that actuation of the accelerator control changes the switch position from its idle validation position to its throttle validation position according to a given, and often very precise, calibration. The electronic fuel control system ignores the throttle control signal until it receives a throttle validation signal by way of the switch.
Accordingly, if an erroneous in-range throttle signal arrives at the electronic fuel control system, unintended fuel delivery is avoided because the electronic fuel control system has not yet received a throttle validation signal.
The idle validation switch attaches to the accelerator pedal or hand control as a separate component. The switch slidably and separately mounts to the accelerator control device in such manner to provide the switching point at a particular pedal or hand control lever position. It is necessary to adjust or calibrate the point at which the switching occurs to coincide with a specified throttle signal level, i.e., a point of transition between idle and throttle operation. This insures that the switch is in the idle valid mode when the driver releases the accelerator control device, and that the engine will have a smooth idle to power transition when the driver applies the throttle. Switch transition points are typically specified by the engine manufacturer.
Installation of the separate idle validation switch can be difficult because of the sensitive calibration required to meet the engine manufacturer's specifications, and the complex test procedures needed to insure that proper switch functioning occurs. Additionally, the switch must meet stringent environmental quality standards to function reliably in typical operating environments.
The calibration requirements of the separately mounted idle validation switch of Lundberg can expose a trucking concern to potentially thousands of dollars in costs in the event of switch failure. Consider a situation where a truck driver encounters a failure of such throttle equipment while in route. The truck driver would likely tow the truck to an authorized repair service and not only obtain the parts necessary to replace the pedal assembly, but also employ a qualified repair person to accomplish the necessary calibration between the separate idle validation switch and the throttle position sensor. As may be appreciated, the time and money lost in accomplishing such repairs can be significant.
These factors result in an expensive throttle control with validation switch and, in some cases, marginal product reliability. The resulting product is also virtually impossible to service in the field without extensive expert calibration. In some cases the entire accelerator control assembly is necessarily replaced. Such difficult field service further adds to the overall cost of such throttle validation systems.